The Mexican revolution, beginning in 1910, evolves as a long and complex sequence of violent events lasting ten years. By May 1911 it has acquired sufficient impetus for the ageing dictator Díaz to be compelled to resign. He escapes into exile. Francisco Madero is elected president.

Madero's moderate policies please no one. In 1913 he is toppled and murdered in a coup led by the army commander, Victoriano Huerta. Huerta's assumption of the presidency restores the condition of dictatorship from which the country has so recently escaped. But he is rapidly deposed in 1914, in a coup which is immediately followed by civil war.

Two of the main contenders in the civil war are romantic figures in a Mexican bandit tradition. Pancho Villa, son of a labourer and a fugitive from justice from an early age, forms a private army several thousand strong which becomes known as the Division of the North.

Emiliano Zapata, also the son of a peasant, wins a reputation among the dispossed of southern Mexico for leading peasant groups in the seizure of land (using a famous slogan Tierra y Libertad, 'Land and Liberty'). He too becomes the commander of a guerrilla force numbering eventually some 25,000 men - the Liberation Army of the South.

Both men fight on behalf of Madero in the early stage of the revolution in 1911. Both take part in the toppling of Huerta in 1914. But there is also a third and more conventional group in the struggle against Huerta. This is a moderate political party, known as the Constitutionalists and led by a landowner, Venustiano Carranza.

Once victory over Huerta has been jointly achieved, civil war develops between these three groups of former allies. Usually, but not always, the conflict is between the two guerrilla leaders on one side and the Constitutionalists on the other.

In November 1914 Villa's and Zapata's armies together occupy Mexico City (where the citizens are impressed by the courteous ways of these peasant guerrillas). But over the next two years it is Carranza's forces which gradually prevail. By May 1917 he is in a strong enough position to be formally elected president.

The election takes place under the terms of a radical new constitution of 1917, promising extensive measures of land and labour reform. Carranza, conservative by nature, probably has little intention of delivering these reforms. But his scope for action is anyway limited by a continuing guerrilla campaign against his regime, carried out by Villa and Zapata.

These years of unrest are brought to an end in 1920 when a swift and effective coup against Carranza is carried out by one of his best generals, Alvara Obregón. Obregón's own election as president, in December 1920, ushers in a welcome period of calm after the decade of ceaseless revolution.

The main rivals in the civil war all come to a violent end. Zapata is tricked, in April 1919, into attending a meeting where he is ambushed and shot by Carranza's troops. Carranza is murdered in May 1920 while attempting to flee to Veracruz. Villa is granted a pardon by Obregón on condition that he retires to his ranch, where he is assassinated in 1923.

Obregón and Calles: 1920-1928

During the years of the revolution Obregón has been the most successful soldier in Mexico, regularly winning victories on behalf of Carranza, but he has also been a consistently radical voice in the politics of the time. In any area where he establishes control, against the forces of either Villa or Zapata, he introduces minimum wages and maximum hours for labour and takes measures to restrain the church.

Such policies also characterize his four years in office, when he begins to put into effect the reforms envisaged in the constitution of 1917 (in the shaping of which Obregón has himself been a powerful influence on the radical side).

An administrative framework is set up for the redistribution of land to the peasants (a modest beginning is made with some 3 million acres), educational programmes are initiated, support is given to organized labour and measures are taken against the church. Obregón continues to display his other skill, as a general, when he marches in 1923 to defeat a right-wing rebellion which has the tacit support of at least half the army.

At the end of his term, in 1924, Obregón is succeeded as president by his friend (and his secretary of the interior), Plutarco Elías Calles.

Calles continues Obregón's policies (a further 8 million acres are redistributed in the programme of land reform). His term in office sees the first effective reaction by the church to the anti-clerical policies of the revolution. In 1926 the clergy adopt a weapon more normally associated with industrial workers. They go on strike. For nearly three years not a single church service of any kind is held in Mexico, though the buildings themselves remain open for prayer.

During this period there is also a more violent and dramatic manifestation of religious reaction.

In 1928 Obregón is again elected president, in a sequence which already seems to be assuring unprecedented continuity for the party of revolution - though this year's elections are marred by the use of terror and violence by both revolutionary and conservative supporters.

Shortly after the election Obregón is attending a private victory celebration when he is shot by a Roman Catholic assassin outraged at the recent anti-clerical policies. But Obregón's death does nothing to halt the progress of his faction. Instead, it is given lasting presence in Mexican political life when Calles establishes, in 1929, the National Revolutionary party.

A party by any other name: from1929

The party founded by Calles in 1929 retains power in Mexico for seventy-one years, albeit under a succession of different names. It starts as the PNR (Partido Nacional Revolucionario, National Revolutionary Party), becomes in 1938 the PRM (Partido Revolucionario Mexicano, Mexican Revolutionary Party) and in 1946 acquires its lasting name as the PRI (Partido Revolucionario Institucional, Institutional Revolutionary Party).

Just as a rose by any other name would smell as sweet, the revolutionary party remains one and the same. Since it wins by a wide margin every presidential election to the end of the 20th century, Mexico becomes effectively a one-party democracy. Party nomination for the presidency is tantamount to election.

As in any political system (unless totalitarian) there are regular and open disagreements about policy. But these develop in Mexico as left-wing and right-wing factions within the PRI. As different groups within the party gain influence, national policy shifts accordingly.

For most of the period from 1929 the chosen model is a centrally directed economy in which measures of reform are introduced gradually. The redistribution of land, for example, is for much of the period a slow but continuing process. By 1940 about 115 million acres have been divided among peasants (even so, more than this remains in private hands in the large estates). During the 1960s another 40 million acres are redistributed.

The major turning point in the Mexican economy is the nationalization, by Lázaro Cárdenas in 1938, of the holdings of the foreign oil companies (the immediate pretext is their refusal to comply with the wages and conditions for their workers demanded by Cárdenas and his reforming government).

The possession of oil brings Mexico increasing prosperity after World War II. It opens the doors of international banks, whose loans fund ambitious programmes of industrialization. Vast new reserves of oil are discovered in 1976 in the Tabasco and Chiapas regions. The proceeds are confidently expected to service an international debt amounting by this time to some $80 billion.

However this rapid growth in the economy is accompanied by the familiar perils of high unemployment, high inflation, a falling exchange rate and the flight of capital as wealthy Mexicans invest more securely abroad. In 1976 José López Portillo, the newly elected president, nationalizes the banks and imposes tight currency controls.

The situation is made worse by the collapse of world oil prices in the 1980s. Meanwhile the effect of long single-party rule is beginning to be reflected in increasing charges of corruption. To add to these problems, an earthquake devastates Mexico City in 1985, killing some 7000 people. Circumstances are conspiring to tarnish the undeniable achievements of the PRI.

Opposition and Zapatistas: the 1990s

During the 1980s there is the first sign of an opposition party which can claim some long-term chance of success against the RPI. Representing right-wing interests, it is known as the PAN (Partido de Acción Nacional, National Action Party). By the 1990s there is also another effective party of opposition in the form of the PRD (Partido de la Revolución Democrática, Party of the Democratic Revolution).

Continuing crises, both economic and political, give the ruling PRI an incentive to cooperate with these emerging parties in improving Mexico's democracy.

On the economic front the PRI's long-standing commitment to a centralized state economy begins to be dismantled during the 1990s by measures of privatization - the panacaea of the period in many parts of the world. But Mexico's status as an emerging capitalist economy is shaken by two crises. A devaluation in 1994 gets out of control and leads to a collapse in the stock market. The situation is only recovered during 1995 by IMF support and a stringent austerity programme.

A similar collapse of stock market and of peso occurs in November 1997 in the wake of the Asian financial crisis. Again international support averts disaster.

In political terms the main crisis of the 1990s is the emergence of various groups of guerrillas. The first is the ZNLA (Zapatista National Liberation Army), which in 1994 seizes towns in the southern state of Chiapas and demands work and welfare for Mexico's poverty-stricken population of Maya Indians. Government efforts to negotiate an end to Zapatista insurgency continue through the rest of the decade, but without any final resolution.

Meanwhile, the ruling party is rocked by two assassinations in 1994. The victims are the party's presidential candidate (Luis Donaldo Colosio) and secretary-general (José Francisco Ruiz Massieu). The disaster is compounded by widespread suspicion that the murders have been carried out on behalf of rivals high within the PRI itself, with possible links to Mexico's drug mafia.

These various circumstances induce the PRI to agree measures of electoral reform with the opposition parties, ensuring at least that elections henceforth are fairly conducted and properly supervised (something never previously to be relied upon).

Voting takes place on the new basis for the mid-term elections in 1997, and the result is a sensational first dent for nearly seventy years in the single-party dominance of Mexican politics. The PRI retains control of the senate and remains the largest party in the chamber of deputies, but it loses control of the lower chamber to a coalition of its opponents.

The president of Mexico, elected in 1994, is Ernesto Zedillo Ponce de León (who replaced Colosio as the PRI candidate when Colosio was assassinated on the campaign trail in March 1994).

The shift in Mexico's long-established political order continues dramatically in the presidential election of July 2000. Vicente Fox, leader of the centre-right PAN (National Action Party) wins by a convincing margin over the PRI candidate, Francisco Labastida. For the first time in seventy-one years the government of Mexico is in the hands of a politician outside the revolutionary party founded by Plutarco Elías Calles in 1929.

The most dramatic event early in Fox's presidency is the peaceful march on Mexico City in March 2001 by the Zapatista Liberation Army, led by Subcomandante Marcos. Laying down their arms after seven years of insurgency, the guerillas hope to achieve the passage of a bill of rights by negotiation with the president.